Over the past decade, a significant amount of research has been directed towards the development of high performance and small size MEMS gyroscopes for consumer electronics applications. MEMS gyroscopes have also been investigated for inertial navigation systems, particularly for situations where GPS navigation will not function. For inertial navigation, the primary challenge is limiting the accumulation of angular error over time. Many MEMS gyroscopes operate in rate mode. In this mode, gyroscopes measure angular velocity, which must be computationally integrated over time to determine an angle of rotation. This produces integration errors that must be periodically recalibrated by, in some cases, an assisting GPS unit.
Whole angle gyroscopes, also referred to as rate integrating gyroscopes (RIGs), are capable of detecting an angle of rotation directly, eliminating the need for computational rate integration over time. Moreover, the dynamic range and bandwidth of a RIG are larger than rate gyros. Whole angle mode operation requires resonators that, once excited with a vibration, allow the vibration pattern to precess freely around the resonator as the device rotates. For this reason, the resonator must have a long ring-down time, a characteristic associated with low resonant frequencies and high quality factors (Q). These features make micro-fabrication of such sensors in small size challenging. Since resonant frequencies typically are inversely proportional to the size of the resonator, extreme miniaturization can significantly increase the resonant frequency of the resonator. For this reason, commercially available ultra high Q RIGs are usually golf-ball sized or larger.
RIGs must also be symmetric about an axis to allow a vibration to precess freely around the resonator as the device rotates. Several axisymmetric microstructures, such as rings, cylinders and disks, have been investigated to implement MEMS gyroscopes. Each of these has been unable to achieve the high Q and low resonant frequency necessary for whole angle mode operation. In contrast, the three dimensional shell structure of a micro-hemispherical resonating gyroscope (μHRG) can obtain a resonant frequency much lower than the frequency range of other MEMS structures. Further, due to the absence of sharp corners and the characteristic energy distribution pattern, a μHRG has the potential to reach ultra-high Q.
Successful fabrication of μHRGs by conventional semiconductor fabrication processes would enable low-cost fabrication of integrated μHRGs. Additionally, by using such processes, μHRGs can be constructed using higher levels of system integration. Aspects of the present disclosure enable the creation of μHRGs having a low resonant frequency and ultra-high Q using foundry-compatible fabrication techniques. Some embodiments of the present disclosure satisfy requirements to operate in whole angle mode. Some embodiments of the present disclosure are also suitable for use in rate mode.